Some of the company’s and individuals’ money pertains to interest-based businesses like NBFC, DFI, and AMC funds not always but 90% of deposits of these companies are interest base. Then Islamic Bank reinvests these deposits into different projects. The quest is whether the profit generated by Islamic Bank which they further distribute to their lenders shariah-compliant or not? Definitely, it turns out to be Haram if the gains are from companies that themselves rely on capitalism and/or do prohibited stuff trade. Also, banks are selling and buying currency notes which is totally haram. In Islamic banks, also sell and buy currency notes.
A lame remark often encountered by those opting for Islamic banking: